As illustrated in FIG. 10, it is considered to introduce an operation of a mobile communication system in which a macro radio base station MBS (Macro Base Station, also referred to as “eNodeB” or “eNB”) and a femto radio base station FBS (Femto Base Station, also referred to as “HeNB” or “HNB”) are mixed.
In this case, a mobile station that communicates with the macro radio base station MBS is referred to as “macro mobile station MUE (Macro User Equipment)” and a mobile station that communicates with the femto radio base station FBS is referred to as “femto mobile station FUE (Femto User Equipment)”.
Further, a cell under the control of the femto radio base station FBS may also be referred to as “CSG (Closed Subscriber Group) cell”. In the CSG cell, connection is permitted only to a specific mobile station belonging to the CSG. An example therefor is that the CSG is set to each family and only the family is permitted to connect to the CSG cell installed at their home. In the CSG cell, the mobile station to which the connection is permitted is limited to the CSG member. Given this fact, it is easily imaged a case where a mobile station with no access right to the CSG cell is present in the vicinity of the CSG cell and a communication is performed by connecting to another cell, e.g., a cell under the control of the macro radio base station MBS.
Thus, in an environment where the femto radio base station FBS and the macro radio base station MBS are mixed, there is a case where the macro mobile station MUE exists within the coverage of the femto radio base station FBS.
However, the above-described mobile communication system has a problem in that when the macro radio base station MBS and the femto radio base station FBS are operated in the same frequency band, it is probable that a significant quality deterioration or a capacity decrease occur.
Particularly, when the macro mobile station MUE is present in the vicinity of the femto radio base station FBS, interference between the macro mobile station MUE and the femto radio base station FBS is a problem.
Particularly, when the macro mobile station MUE does not have the access right to the CSG cell under the control of the femto radio base station FBS and performs a notification in the immediate vicinity of the femto radio base station FBS, an interference between the macro mobile station MUE and the femto radio base station FBS is a serious problem.
In the example of FIG. 10, even in the case of the macro mobile stations MUE1 and MUE2 connecting to the same macro radio base station MBS, the interference between the macro mobile station MUE 2 and the femto radio base station FBS is not a serious problem because the distance between the two is large; however, the interference between the macro mobile station MUE1 and the femto radio base station FBS is a serious problem because the distance between the two is small.
For example, when the macro mobile station MUE1 transmits an uplink signal, if the femto mobile station FUE transmits an uplink signal at the same time by using the same radio resource, then the femto radio base station FBS experiences the interference from the macro mobile station MUE1 and thus it is probable that the uplink signal from the femto mobile station FUE cannot be correctly received.
Similarly, when the macro mobile station MUE1 receives a downlink signal from the macro radio base station MBS, if the femto radio base station FBS transmits the downlink signal to the femto mobile station FUE at the same time by using the same radio resource, then it is probable that the macro mobile station MUE1 cannot correctly receive the downlink signal from the macro radio base station MBS.
Therefore, the present invention is intended to overcome the above-described problem. An object of the present invention is to provide a mobile communication method and a radio base station, capable of inhibiting an influence of an interference in a mobile communication system where a macro radio base station MBS (first radio base station) and a femto radio base station FBS (second radio base station) are mixed.